This problem started with my upgrade to MacOS High Sierra on a Mac Pro 2012. Eizo CG 243W second monitor, LG as desktop and menus monitor.
Since upgrading to High Sierra, I have noticed that images displayed in Safari *may* turn black (sometimes after a short delay) if viewed on the Eizo, but when the browser window is dragged across to the main monitor (a humble LG), the images re-appear. It does not matter if I swap the monitor functions round in System Preferences - the Eizo remains the locus of the problem..
Facebook is particularly susceptible to this problem.
This problem does not appear if I use other browsers like Firefox or Brave. Images in other programs such as Photoshop or Preview appear as they should.
Any suggestions?
PS. I *think* the problem may be related to the profile generated by my Spyder5 in combination Eizo's Color Navigator software.